1. Field of the Invention
The present invention relates to an organic light emitting display and a driving method thereof.
2. Discussion of Related Art
Recently, various flat panel display devices having reduced weight and volume in comparison to cathode ray tubes (CRTs) have been developed. Types of flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting display, etc.
An organic light emitting display displays an image using organic light emitting diodes that generate light through recombination of electrons and holes. The organic light emitting display has an advantage over other flat panel display devices in that it has a high response speed and is driven with low power consumption.
FIG. 1 is a circuit view showing a pixel of a conventional organic light emitting display.
Referring to FIG. 1, a pixel 4 of a conventional light emitting display includes an organic light emitting diode (OLED) and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is coupled to the pixel circuit 2 and a cathode electrode of the OLED is coupled to a second power supply ELVSS. The pixel circuit 2 controls an amount of current supplied to the OLED in accordance with a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. To this end, the pixel circuit 2 includes a second transistor M2 coupled between a first power supply ELVDD and the OLED, a first transistor M1 coupled between the second transistor M2, the data line Dm, and the scan line Sn, and a storage capacitor Cst coupled between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 is coupled to the scan line Sn and a first electrode of the first transistor M1 is coupled to the data line Dm. Further, a second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. Here, the first electrode may be either a source electrode or a drain electrode and the second electrode may be the other one of the source electrode or the drain electrode. For example, if the first electrode is the source electrode, the second electrode is the drain electrode. The first transistor M1 is turned on when the scan signal is applied at its gate to supply the data signal supplied from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst charges a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one side of the storage capacitor Cst and the first electrode of the second transistor M2 is coupled to the other side of the storage capacitor Cst and the first power supply ELVDD. Further, a second electrode of the second transistor M2 is coupled to the anode electrode of the OLED. The second transistor M2 controls the amount of current flowing from the first power supply ELVDD to the second power supply ELVSS via the OLED in accordance with the voltage value stored in the storage capacitor Cst. At this time, the OLED generates light corresponding to the amount of current supplied from the second transistor M2.
The conventional organic light emitting display may not display an image with desired luminance due to the change in efficiency according to the deterioration of the OLED. In practice, the OLED is deteriorated over time so that light with gradually low luminance is generated in response to the same data signal supplied through the data line Dm.